This paper deals with a computational method based on multiphase modeling to predict the interactions between free-surface flows and linear elastic objects that undergo finite deformations. In multiphase modeling, a field consisting of gas, liquid and solid phases is treated as the immiscible and incompressible fluid-mixture with different physical properties and the governing equations are derived with one-fluid modeling, while the solid model is derived with objective stress rates and discretization in FEM to deal with the finite deformations. Applying the proposed computational method to experimental results, it was shown that the time histories of the displacements of an elastic plate and the fluid forces caused by wave-induced flows are successfully predicted and that the differences of the fluid forces acting on elastic and rigid plates are reasonably predicted.